The present invention relates to a multi-hole tube extrusion die and a multi-hole tube made with the multi-hole tube extrusion die.
A multi-hole tube is flat in cross section, has a multiplicity of holes extending in the longitudinal direction thereof and is used in an evaporator in an air conditioning system of an automobile, and the like. Such a multi-hole tube is disclosed, for example, in Japanese Utility Model Examined Publication No. 2-45729. The multi-hole tube disclosed in this publication has the holes each of which is gradually reduced in cross sectional area from the air intake side of the tube toward the air discharge side thereof to improve processability and strength. Further, the partition wall between adjacent holes is also formed such that it is gradually made slender from the air intake side toward the air discharge side.
Typically, the multi-hole tube is made by hot extrusion using a die (including a rotary wheel type continuous extrusion). Japanese Patent Unexamined Publication No. 3-193209 discloses an example of a multi-hole tube extrusion die. This publication discusses an inclination or approaching angle from the proximal end of the molding portion of a die toward the extreme end thereof to ensure good extrudability.
A typical example of a multi-hole tube extrusion die will be described with reference to FIGS. 10 and 11. The die is composed of a female die 1000 having a flat opening 1001 formed therethrough and a mandrel 1003. The mandrel 1003 has a multiplicity of comb-teeth-like molding portions (hereinafter, referred to as comb-teeth) 1002 which are arranged in a row widthwise in the opening 1001. A material to be processed, which has been heated into a hot state, is extruded through spaces between the opening 1001 and the comb-teeth 1002 to form a multi-hole tube. The flow of the material is indicated by the arrow of a solid line in FIG. 11.
In recent years, apparatuses such as a heat exchanger using multi-hole tubes is improved to be more efficient, and each multi-hole tube is required to be made small in size and have a still greater number of holes than those of a conventional multi-hole tube. A multi-hole tube for satisfying this requirement is constructed such that the width of each hole or flow path is narrow and a partition wall between adjacent holes is thinner than, for example, the outer peripheral wall of the multi-hole tube. Further, in a multi-hole tube extrusion die for use to this end, the comb-teeth 1002 have to be small in cross sectional shape to form a greater number of holes in the multi-hole tube, and the rigidity of the comb-teeth is lessened.